Hot-melt adhesives are used extensively for sealing cases and cartons progressing along an automated assembly line. U.S. Pat. No. 4,602,741 to Faulkner et al. teaches a multi-nozzle manifold assembly for depositing a pattern of parallel beads of adhesive along the surface of a carton flap. The flap may then be closed against a second flap to seal the carton.
In certain applications, it is necessary to apply parallel beads of adhesive having different lengths. For example, in order to seal one end of a cereal box, typically long beads of adhesive are applied to the major flaps of the box, while shorter beads are applied to the minor flaps. At times, a single flap may even have beads of different lengths.
One method of applying adhesive beads of different lengths is to provide a number of closely spaced adhesive dispensing stations along the path of the assembly line, with each station applying adhesive beads of the different lengths. A problem with such a setup is that the adhesives used in assembly line applications have a short set time in order to minimize the time required for assembly line carton sealing. Consequently, the adhesive undergoes some solidification as a carton travels between the dispensing stations.
A second method is described in U.S. Pat. No. 5,024,709 to Faulkner et al., which teaches an adhesive applicator in which a single dispensing station has a number of individually controlled devices to simultaneously apply adhesive. Thus, adhesive applied at one station does not begin to solidify as it moves to a second station. However, such a station requires a number of separate connections to one or more melt units which supply adhesive to the station. A preferred assembly would be one in which there is a single flow path from the melt unit to a multi-nozzle assembly having nozzles that can be individually controlled. One difficulty in the design of such an assembly is that it increases the likelihood of regions of stagnant adhesive along the flow path from the melt unit to the nozzle outlets. In the Faulkner et al. patents identified above, adhesive enters an applicator body at the back of a solenoid armature that is selectively displaced to start and stop adhesive flow to nozzle outlets. Thus, the flow is a linear, coaxial flow along the armature used to control flow. A linear flow path is less susceptible to creation of stagnant regions than a path that includes one or more angles.
Hot-melt adhesive degrades at a relatively rapid pace. For this reason, creation of eddies and regions in which no flow occurs is undesirable. While the linear flow along a solenoid armature reduces the likelihood of stagnant regions, requiring a linear flow along each solenoid armature of an assembly having a number of individually controlled devices reduces the modularity and compactness of the assembly.
U.S. Pat. No. 4,687,137 to Boger et al. teaches an adhesive dispensing apparatus which is different than the Faulkner et al. devices in that Boger et al. describes a modular assembly in which adhesive is fed partially down the length of an armature. However, a difficulty encountered in such an arrangement is that as the adhesive is fed to the intermediate region of the armature, there is an equal tendency for the adhesive to progress rearwardly along the armature as there is for the adhesive to move forwardly toward an outlet port. This tendency to move rearwardly can cause eddies and stagnant regions. Boger et al. teaches limiting the adhesive-receiving chamber along the armature to include only a small volume that is rearward of the adhesive feed. However, the potential of adhesive degradation occurring within this chamber is still significant. Moreover, sealing the chamber to prevent the leak of hot-melt adhesive along the armature is a difficult task, particularly for applications in which a low-friction seal is required to allow free movement of the armature during high speed activation and deactivation. U.S. Pat. No. 4,711,379 to Price teaches use of a pair of packing structures to seal the rearward portion of an armature.
It is an object of the present invention to provide a device for controlling the intermittent flow of adhesive material in which modularity and compactness are enhanced without an increased susceptibility to creation of eddies and stagnant regions which would promote adhesive degradation.